For fans of World TeamTennis, the mixed-gender summer league, the Washington Kastles are the cream of the crop. Formed in 2008 (WTT has existed since 1973), the Kastles have won six league championships, the latest one coming in 2015. In 2011, the team went undefeated—then did it again, along the way amassing the longest winning streak in professional team sports history. The Williams sisters, Kevin Anderson, Martina Hingis and Nick Kyrgios have all donned the Kastles' iconic red, among other star players.

Now, the team has a stadium worthy of its illustrious name. The new court is on the roof of Union Market in Washington D.C., which not only provides a great view of the action, but also of the Market District in the nation's capitol.